AC/DC Converter COT Control and Flip-Chip Packaging
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Solution Overview
Problem
Conventional AC/DC converters for high power density charging face limitations in power density due to large transformer and capacitor sizes, leading to slow transient response and increased EMI noise, which complicates achieving compact and efficient charging solutions.
Innovation Solution
The implementation of a secondary side constant-on-time (COT) control scheme with a comparator-based feedback loop on the secondary side, allowing for higher switching frequencies up to 150 kHz, reduced transformer turns, and MOSFET flip-chip packaging to integrate the main switch and control IC on a single die paddle, enabling smaller component sizes and improved thermal dissipation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional PWM control fly-back AC/DC converter is used, then the transformer and capacitors can transfer energy reliably, but the transformer and capacitor sizes become large leading to low power density
Solution Approach 1:
The patent changes the control parameter from conventional PWM with bandwidth limited to one-tenth of switching frequency to COT control with bandwidth extending to one-half of switching frequency. This parameter change enables the system to operate at higher switching frequencies (65-85 kHz extended to higher ranges), which directly reduces transformer and capacitor sizes while maintaining reliable energy transfer. The COT control scheme achieves this by using a comparator-based feedback loop that responds twice as fast as conventional PWM controllers.
2Volume of moving object
If higher switching frequency is implemented to reduce component size, then transformer and capacitor sizes decrease, but EMI noise increases
Solution Approach 1:
The patent converts the harmful EMI noise generated by high dv/dt drain voltage into a beneficial outcome by implementing a PCB layout where the large copper pad for thermal dissipation is electrically isolated from high voltage nodes. The MOSFET drain is connected to a small copper pad, while the large copper pad is dedicated to thermal dissipation and connected to ground or low voltage nodes. This layout converts what would be EMI noise from the large thermal pad into a thermal management solution, while the high voltage switching occurs on the small isolated pad where EMI is contained.
3Temperature
If large copper pad area is used for thermal dissipation, then thermal performance improves, but EMI noise increases due to large drain lead area
Solution Approach 1:
The patent segments the copper pad functionality into distinct regions: a small copper pad for high voltage drain connection (EMI containment) and a large copper pad for thermal dissipation (connected to ground or low voltage). This segmentation separates the thermal management function from the high voltage switching function, allowing the large copper area to serve thermal purposes without generating EMI noise, while the small isolated pad handles the high dv/dt switching events.
4Loss of energy
If conventional PWM control with CCM and DCM mode switching is used to maintain efficiency, then conversion efficiency is maintained across load conditions, but device complexity increases due to extra compensation loops and components
Solution Approach 1:
The patent implements a universal COT control scheme that maintains high conversion efficiency across all load conditions (from light to full load) without requiring separate CCM and DCM control loops. The constant-on-time control inherently adapts to load conditions by adjusting the off-time based on the energy transfer requirements, eliminating the need for complex mode switching logic and compensation circuits while maintaining optimal efficiency throughout the operating range.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach results in a compact charger with enhanced power density exceeding 0.5 W/CC, reduced EMI noise, and improved thermal performance without additional components, achieving fast transient response and stable output voltage during load transitions.
Implementation Method 1
A transformer TX1 transfers energy received from a primary side source to a secondary side to power a load
Implementation Method 2
The transistor has drain electrode D located on a bottom surface of a transistor die connected to a die paddle of a lead frame
Data Source
AI summary
A charger comprises a housing, a first multi-layer printed circuit board (PCB), a second multi-layer PCB, and a third multi-layer PCB. The first PCB comprises at least a portion of a primary side circuit. The second PCB comprises at least a portion of a secondary side circuit. The third PCB is perpendicular to the first PCB and the second PCB. An isolation coupling element is disposed on the third PCB. The isolation coupling element comprises a multi-layer PCB. The first PCB comprises a high voltage (HV) semiconductor package. A surface of a die paddle of the HV semiconductor package is exposed from a molding encapsulation of the HV semiconductor package.